Gun sight compensator

ABSTRACT

A range compensator for a gun sight for an associated gun is provided. The compensator includes at least one Risley prism pair that is rotatable in opposite relative directions about a common axis; mounting means for mounting the Risley prism pair to the sight between the sight and a target at a distance; and, a respective rotator associated with the Risley prism pair for rotating each prism in the Risley prism pair about the axis that is generally aligned with the path. The prisms are rotatable between an unrefracted range finding position in which a “line of departure” required to ensure the projectile strikes the target is determined and a refracted firing position in which the path of light extending between the sight and the target is refractively deviated to maintain the target centered with the sight when the gun is positioned along the required “line of departure”.

FIELD OF THE INVENTION

The present invention relates to a gun sight compensator.

BACKGROUND OF THE INVENTION

The trajectory for any projectile, except for self-propelled ones, follows a repeatable pattern when all variables are held constant. Rather than following a flat trajectory, all projectiles drop downwards due to the effects of gravity. The downward displacement at various distances (i.e., the amount of drop) depends largely on the ballistics of the projectile. Other forces influencing the drop dynamics include temperature, humidity, altitude, windage, and angle of fire. In addition, there are several forces that potentially affect the lateral displacement of a projectile relative to the firing direction, primarily windage (especially crosswinds) and any oblique aiming posture or “canting”.

The aggregate impact of all these factors is that the actual projectile flight path deviates in an estimable manner (magnitude and direction) from a straight line of sight. The final deviation can be expressed as having two linear components, one vertical (altitudinal) and one lateral (horizontal); i.e., bullet drop and windage, respectively. Experienced shooters and ballistics experts commonly generate experience-based tables that provide reliable elevation and windage predictions and compensations for all anticipated target distances and shooting conditions. The consequential displacements in both vertical and horizontal planes are offset using compensatory height and lateral sight adjustments. Commonly, horizontal and vertical reticules within a sight associated with a gun are displaced to allow the shooter to sight “on target.” The reticules are moved so they coincide to where the shooter calculates the bullet will impact and the shooter realigns the weapon so that the adjusted reticules point at the desired target.

An Adjustable Ranging Telescope (ART) uses a different approach. An adjustable cam is used to realign the scope (or “sight”) relative to the gun so that the whole scope is tilted variably downwards to compensate for the anticipate bullet drop and the sighting reticule remains in a centrally fixed position. The deficiencies of an ART, as reported in Death From Afar, Volume 3, The Black Book III by Lt. Col. Norman A. Chandler, USMC (Ret), and Roy F. Chandler. (Iron Brigade Publishing; (Nov. 1, 1994). Page 94. and Modem Sniper Rifles by Duncan Long Paladin Press; (June 1988) Page 77, include some unreliability with tracking and return to zero operations. Also, the bullet drop compensation is cammed and coupled with the ranging and magnification wheels. This allows no independent control over magnification at the time of firing unless the shooter uncouples the scope ring before adjusting the magnification.

Another approach involves changing the field in front of the reticules of the scope. The objective optics of the telescope creates a virtual image that is centered in the scope. Prisms are used to decentre the area being sampled, thereby displacing the field upon which the reticules are overlaid. The impact of this prismatic displacement will be a function of the magnification of the system. In other words, the prism power required to produce the same target acquisition effect for a 10× sight will be five times that required for a 2× sight. This greatly complicates any control. Further, the prism can only produce displacement “windows” within the confines of the image that is available. The total displacement that is achievable will be a function of the imaging optics in front of the prism itself. Additional prismatic power will only reveal the inside wall of the telescope, rather than a more peripheral view of the real world.

There remains a need for a gun sight compensator that can be adjusted easily and can displace the target image over a larger viewable area.

SUMMARY OF THE INVENTION

A range compensator for a gun sight for an associated gun is provided. The compensator includes at least one Risley prism pair that is rotatable in opposite relative directions about a common axis; mounting means for mounting the Risley prism pair to the sight between the sight and a target at a distance; and, a respective rotator associated with the Risley prism pair for rotating each prism in the Risley prism pair about the axis that is generally aligned with the path. The prisms are rotatable between an unrefracted range finding position in which a “line of departure” required to ensure the projectile strikes the target is determined and a refracted firing position in which the path of light extending between the sight and the target is refractively deviated to maintain the target centered with the sight when the gun is positioned along the required “line of departure”.

The range compensator may further include a range finder that determines the target distance; a processor that receives the distance measurement and communicates it to a prism rotation retrieval and storage means, which provides the degree of prism pair rotation required for rotating the prisms of the Risley prism pair to the refracted firing position and communicates the required degree of prism pair rotation to the processor. A controller that is operably connected to the rotator communicates with the processor, receives the required degree of prism pair rotation and effects rotation of the prisms to the refracted firing position.

The rotator may effect rotational shift by a combination of co-rotation and counter-rotation of the Risley prism pair.

The rotator may include first and second motors. The first motor is rotationally coupled to both prisms in the Risley prism pair to cause equal but directionally opposite rotation of the prisms about the axis and the second motor is rotationally coupled to both prisms to cause simultaneous and equal co-rotation of the prisms.

LIST OF FIGURES

Preferred embodiments of the present invention are described below with reference to the accompanying drawings in which:

FIG. 1 is a schematic view illustrating a gun sight compensator according to an embodiment of the present invention;

FIG. 2 is a schematic view illustrating the gun sight compensator according to a preferred embodiment of the present invention;

FIG. 3 is a schematic view illustrating the gun sight compensator of the present invention in use;

FIG. 4(a) is a schematic view of a Risley prism pair according to the present invention in which the component prisms are positioned in a refracted orientation;

FIG. 4(b) is a schematic view of the Risley prism pair according to the present invention in which the component prisms are positioned in an unrefracted orientation;

FIG. 5(a) is a schematic view looking through the Risley prism pair according to the present invention in which the component prisms are positioned in a lateral unrefracted orientation;

FIG. 5(b) is a schematic view looking through the Risley prism pair according to the present invention in which the component prisms are positioned in a lateral downwardly refracted orientation;

FIG. 5(c) is a schematic view looking through the Risley prism pair according to the present invention in which the component prisms are positioned in a lateral upwardly refracted orientation;

FIG. 6(a) is a schematic view looking through the Risley prism pair according to the present invention in which the component prisms are positioned in a vertical unrefracted orientation;

FIG. 6(b) is a schematic view looking through the Risley prism pair according to the present invention in which the component prisms are positioned in a vertical rightwardly refracted orientation;

FIG. 6(c) is a schematic view looking through the Risley prism pair according to the present invention in which the component prisms are positioned in a vertical leftwardly refracted orientation;

FIG. 7(a) is a schematic view of the Risley prism pair according to the present invention in which the component prisms are positioned in a lateral downwardly refracted orientation producing a vertical prismatic shift of a target image;

FIG. 7(b) is a schematic view of the Risley prism pair according to the present invention in which the Risley prism pair, with its component prisms positioned in a lateral refracted orientation, has been rotated to produce a lateral prismatic shift ofthe target image;

FIG. 7(c) is a schematic view of the target image according to the present invention moving from an unadjusted image location to an adjusted image location;

FIG. 8(a) is a schematic view of the Risley prism pair according to the present invention in which the component prisms are positioned in a vertical rightwardly refracted orientation producing a lateral prismatic shift of a target image;

FIG. 8(b) is a schematic view of the Risley prism pair according to the present invention in which the Risley prism pair, with its component prisms positioned in a vertical refracted orientation, has been rotated to produce a vertical prismatic shift of the target image; and,

FIG. 8(c) is a schematic view of the target image according to the present invention moving from an unadjusted image location to an adjusted image location.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an apparatus generally indicated by reference 5 in accordance with a first embodiment of the present invention. Referring to FIGS. 1 and 3, the apparatus 5 is a range compensator for a gun sight 7, which enables the gun sight 7 to appear “on target” when an associated gun 9 is deviated from a path of light or “line of sight” 17 orientation with a target 11 to a “line of departure” 35 orientation to compensate for the trajectory characteristics of a projectile to be launched from the gun 9. The “line of departure” 35 is the line along which the gun is aligned and defines the initial path of the projectile as it “departs” from the gun. It corresponds to the initial part of the trajectory path 34 which is the path followed by the projectile. The compensator 5 creates an accurate trajectory compensated field of view aligned with the target 11, which allows a point of impact, such as the target 11 to be viewed as the projectile is fired from the gun 9.

The expression “gun” herein refers to any ballistic weapon which launches a projectile. Any gun 9 known to those skilled in the art may be employed, such as the Barrett Model 82A1 and Model 95M 0.50 calibre rifles as manufactured by Barrett Firearms Manufacturing, Inc. of Murfreesboro, Tenn., the Remington 700 as manufactured by Remington Arms Co., Inc. of Madison, NC. and the M136AT4 84mm calibre light anti-armour disposable rocket launcher as manufactured by Alliaant Techsystems of Edina, Minn.

The compensator 5 includes one Risley prism pair 13, which consists of two equally powered prismatic lenses 21 and 23 placed in close proximity on counter-rotating mountings (not shown).

The compensator 5 also includes mounting means 15 for mounting the Risley prism pair 13 to the sight 7, between the sight 7 and the target 1 1, to allow refractive deviation of the path of light 17 extending between the sight 7 and the target 11. In an alternate embodiment, the mounting means 15 mounts the Risley prism pair 13 to the gun 9. The mounting means 15 may be of any type known to those skilled in the art, such as clips which clip the compensator 5 to the sight 7 or the gun 9. In an alternate embodiment, the compensator 5 may be screwed directly onto the sight 7 on a mount or on the gun 9. The mounting means 15 may releasably mount the compensator 5 to one of the sight 7 or the gun 9. Alternately, the compensator 5 may be fixedly mounted. In a further embodiment f the invention the compensator 5 may comprise an integral element of the sight 7, fixed o the sight 7 during its manufacture, in which case the mounting means forms part of the sight.

Any sight 7 known to those skilled in the art may be used, such as the UNERTL-10X Tactical from Unertl Optical Company, Inc. of Mars, Pennsylvania, since the compesator 5 acts independently of the type of power of the sighting system being used. For example, if the compensator 5 is used in conjunction with a laser sight, it would provide a programmable deflection of the laser beam that coincides with the path of light 17; i.e., the Risley prism pair 13 refracts the laser beam emanating from the laser sight. Accordingly, the sight 7 employed may include open sights, telescopic sights such as the SN-1/TAR Long Range Precision Counter Sniper Optical System as manufactured by U.S. Optics of Buena Park, Calif., the Leupold VX-II 3-9×40mm Tactical scope as manufactured by Leupold & Stevens, Inc. of Beaverton, Oreg., Laser pointing sights such as the FA-4 ULS aiming laser system as manufactured by Laser Devices, Inc. (LDI) of Monterey, Calif., the L72 Visible Red Laser Sight as manufactured by SureFire LLC of Fountain Valley, Calif., Laser holography sights such as the Bushnell® HOLOsight as manufactured by EOTech, Inc of Ann Arbor, Mich., the The Red Dot C-MORE Tactical sight manufactured by C-More Systems of Manassas, Va., Infrared night vision sights such as the AN/PVS-4 GEN III New System NIGHT VISION Weapon Sight as designed and manufactured by the US military., Electro-optical sights such as the the IRWS 1000 Portable thermal Weapons Sight as manufactured by Sierra Pacific Corp.of Las Vegas, Nev.

The compensator 5 would also work with new emerging sights, such as the video camera gun sight that is currently under development for the US Military's Objective Individual Combat Weapon (OICW). This is a video sight with a zoom lens that is linked to a video display attached to the soldier's helmet, and is being developed by Alliant Techsystems Integrated Defense Co., of Hopkins, Minn. (Graham, is this publicly available information?)

The compensator 5 further includes a rotator 19 associated with the Risley prism pair 13, hich rotates each of the prisms 21 and 23 in the Risley prism pair 13 in opposite relative directions about an axis 25 generally aligned with the path 17 and thereby causes refractive deviation. The rotator 19 may also rotate the Risley prism pair 13 about the same axis 25. In an alternate embodiment, a second rotator 37 may be used for rotating the Risley prism pair 13 about the axis 25 while the rotator 19 rotates the prisms 21 and 23 in opposite relative directions.

The compensator 5 additionally includes a processor 27, a range finder 29 (for determining the distance to the target 11 of the gun 9 and communicating it to the processor 27) and trajectory information retrieval and storage means 31 that provides information concerning the trajectory characteristics of the projectile to be fired to the processor 27. The processor 27 retrieves the trajectory characteristics of the projectile, compares it to the distance to target 11 and determines a prism shift corresponding to an amount of refraction necessary to cause the sight 7 to view a location relative to the target 11 where the projectile would be expected to strike at the distance were the gun 9 pointed directly at the target 11. The processor 27 sends a signal to a controller 33, which is operably connected to the rotator 19, to effect the required rotational shift of the prisms 21 and 23 corresponding to the required amount of refraction. The prisms 21 and 23 are rotated between an unrefracted or range finding position in which the “line of departure” 35 orientation required to ensure the projectile strikes the target 11 is determined and a refracted or firing position in which the “path of light” 17 extending between the sight 7 and the target 11 is refractively deviated to maintain the target 11 centered with the sight 7 when the gun 9 is positioned along the required “line of departure” 35.

Referring to FIG. 2, a schematic view of a preferred embodiment of the compensator according the present invention is illustrated. The compensator 59 includes an additional Risley prism pair, Risley prism pair 67, mounted co-axially with Risley prism pair 13. The Risley prism pair 67 also consists of two equally powered prismatic lenses 63 and 65 placed in close proximity on counter-rotating mountings (not shown). The compensator 59 further includes a rotator 61 associated with Risley prism pair 67, which rotates each of the prisms 63 and 65 in the Risley prism pair 67 in opposite relative directions about the axis 25 and thereby causes refractive deviation. A controller 71, which is operably connected to the rotator 61, effects any rotational shift of prism 63 and 65 corresponding to the required degree of refraction. The rotator 61 may also rotate the Risley prim pair 67 about the same axis 25.

The compensator 59 additionally includes the processor 27, the range finder 29 and the trajectory information retrieval and storage means 31 (as described in relation to the compensator 5). In a preferred embodiment, the processor 27 sends a signal to the controllers 33 and 71 to effect the required rotational shift of prisms (21 and 23) and (63 and 65), respectively, corresponding to the required degree of refraction.

Image Shift

Referring to FIGS. 4(a) and 4(b), the prisms 21 and 23 of the Risley prism pair 13 are illustrated. When the prisms 21 and 23 are aligned base 39 of prism 21 to apex 45 of prism 23 and apex 41 of prism 21 to base 43 of prism 23, as illustrated in FIG. 4(b), the prismatic effect is zero and no deviation is produced. As a beam of light 69 passes through the prism 21, its path is refracted by a degree determined primarily by refractive index (n) and apical angle of the prism 21 (actually prism); the refractive index being somewhat wavelength dependent. For example, the index of refraction for flint glass is about 1% higher for blue light than for red light. The variation of refractive index n with wavelength is called dispersion. This factor requires compensation when using prism system in tandem with monochromatic sighting systems such as red laser, green laser or green phosphor displays. The refracted beam of light then enters the prism 23. Since the second prism component 23 is in an opposed orientation to the first prism component, then the path of the beam of light 69 is refracted a second time, but in a direction opposite that of the first prism component. The opposed first and second prism components effectively “cancel” each other out and as a result there is no net refraction of the path of the beam of light. Referring to FIG. 4(a), as the prisms 21 and 23 are counter-rotated equal amounts, a gradually increasing prismatic effect is created having a linear orientation perpendicular to the base-apex orientation in the zero setting. The maximum prismatic effect is created when the prisms 21 and 23 are aligned base 39 of prism 21 to base 43 of prism 23 and apex 41 of prism to apex 45 of prism 23. In this position, the aggregate prism power is equal to the sum of the two prism components 21 and 23.

The direction of the prismatic effect (i.e., whether the image of the target 11 is displaced vertically to compensate for projectile drop or laterally to compensate for windage) is dependent on the initial base to apex orientation of the respective Risley prism pair.

Vertical Shift

Referring to FIG. 5(a), the component prisms 21 and 23 of the Risley prism pair 13 are oriented base to apex laterally (i.e., the base 39 of the prism component 21 is located on the right side of the gun 9 (from the perspective of a person looking through the sight 7) when the compensator 5 is in its mounted position, and the base 43 of the prism component 23 is located of the left side, opposite the base 39). In the unrefracted or (“zero-effect”) orientation, when the sight 7 is position in the “line of sight” 17 orientation, the target 11 appears in the centre of the sight 7 field of vision.

Referring to FIG. 5(b), as the prism components 21 and 23 are counter rotated downwardly (i.e., toward the six o'clock position of the sight 7 field of vision) the image of the target 11 is moved from its previous centre position to a refracted or vertically displaced position opposite the direction of the counter rotation (i.e., upwardly toward the 12 o'clock position of the sight 7 field of vision). The resultant vertical prismatic effect is additive, each prism contributing equally to the degree or amount of image shift. In contrast, the resultant lateral prism effect is zero because the prismatic powers of the component prisms 21 and 23 are equal and opposite.

Referring to FIG. 5(c), as the prism components 23 and 23 are counter rotated upwardly (i.e., toward the 12 o'clock poison of the sight 7 field of vision) the image of the target 11 is moved from its previous centre position to a refracted or vertically displaced position, opposite the direction of the counter rotation (i.e., downwardly toward the 6 o'clock ofthe field of vision). As in the previous upward image shift , the vertical resultant prismatic effect is additive, each prism contributes equally to the degree or amount of image shift. Also, the resultant lateral prisms effect is zero since the prismatic powers of the components prisms 21 and 23 are equal and opposite.

Once the vertical prism shift has been made, a lateral prism shift could also be created by rotating the Risley prism pair 13 assembly clockwise or counter clockwise to produce either a base right or a base left prismatic effect, thereby permitting a single Risley prism pair to accommodate for both windage and drop.

Referring to FIG. 8(a), the component prisms 21 and 23 of the Risley prism pair 13 were initially oriented base-to-apex vertically and have been counter rotated rightwardly to create an leftwardly detracted visual image, the target 11 image has been shifted by an amount corresponding to the lateral shift 49. In order to compensate for other projectile trajectory factors, such as drop, the target 11 image may be adjusted by a vertical shift 47. The target 11 image may be shifted up or down by rotating the Risley prism pair 13 respectively clockwise or counter clockwise be a degree of rotation 73 in FIG. 8(b). As the Risley prism pair 13 is rotated, the target 11 image moves along image rotation path 51. As such, when the Risley prism pair 13 has been rotated by the degree of rotation 73 the target 11 image is located at an unadjusted rotated image location 55. In order for the target 11 image to be located at the required refracted location, the rotated image must be further refracted such that target 11 image is located at an adjusted rotated image position 57. The degree of prism components 21 and 23 further rotation is a function ofthe vertical shift 47 and the lateral shift 49.

Lateral Shift

Referring to FIG. 6(a), the component prisms 21 and 23 of the Risley prism pair 13 are oriented base to apex vertically (i.e., the base 39 of prism component 21 is located on the top of the sight 7 field of vision at the 12 o'clock position and the base 43 of the prism component 23, opposite the base 39). In the unrefracted or “zero-effect” orientation, when the sight 7 is positioned in the “line of sight” 17 orientation, the target 11 appears in the centre of the sight 7 field of vision.

Referring to FIG. 6(b), as the prism components 21 and 23 are counter rotated to the right (i.e., toward the 3 o'clock position of the sight 7 field of vision) the image of the target 11 is moved from its previous centre position to a refracted or laterally displaced position opposite the direction of the counter rotation (i.e., leftward toward the 9 o'clock position of the sight 7 field of vision). The resultant lateral prismatic effect is additive, each prism contributing equally to the degree or amount of image shift. In contrast, the resultant vertical prism effect is zero since the prismatic powers of the component prisms 21 and 23 are equal and opposite.

Referring to FIG. 6(c), as the prism components 21 and 23 are counter rotated to the left (i.e., toward the 9 o'clock position of the sight 7 field of vision) the image of the target 11 is moved from its previous centre position to a refracted or laterally displaced position opposite to the direction of the counter rotation (i.e., toward the right at the 3 o'clock position of the field of vision). As in the previous lateral image shift, the resultant lateral prismatic effect is additive, each prism contributing equally to the degree or amount of image shift. Also, the resultant vertical prism effect is zero since the prismatic powers of the component powers of the component prisms 21 and 23 are equal and opposite.

Once the lateral prism shift has been made, a vertical prism shift could also be created by rotating the Risely prism pair 13 assembly clockwise or counter clockwise to produce either a base top or a base bottom prismatic effect, thereby permitting a single Risley prism pair to accommodate for both windage and drop.

Referring to FIG. 7(a)-(c), the component prisms 21 and 23 of the Risley prism pair 13 were initially oriented base-to-apex laterally and have been counter rotated downwardly to create an upwardly refracted visual image, the target 11 image has been shifted by an amount corresponding to the vertical shift 47. In order to compensate for other projectile trajectory factors, such as windage, the target 11 image may be adjusted by a lateral shift 49. The target 11 image may be shifted to the right or left by rotating the Risley prism pair 13 respectively clockwise or counter clockwise be a degree of rotation 53. As the Risley prism pair 13 is rotated, the target 11 image moves along image rotation path 51. As such, when the Risley prism pair 13 has been rotated by the degree of rotation 53 the target 11 image is located at an unadjusted rotated image location 55. In order for the target 11 image to be located at the required refracted location, the rotated image must be further refracted such that target 11 image is located at an adjusted rotated image position 57. The degree of prism components 21 and 23 further rotation is a function of the vertical shift 47 and the lateral shift 49.

Effecting a Shift

The degree of image shift required (vertical shift 47 or lateral shift 49) is determined by a processor 27, which receives target 11 information from a range finder 29 and retrieves projectile information from a trajectory information storage and retrieval means 31 and on the basis of this information determines the required amount of prismatic shift to ensure that the gun site 7 appears “on target” when the associated gun 9 is deviated to the “line of departure” 35 orientation. In a preferred embodiment, the processor 27 includes input means for wind speed (not shown), which is determined by a wind meter (not shown).

The range finder 29, which determines the distance to target 11, may be any range finder known to those skilled in the art that is able or adaptable to communicate with the processor 27, such as the X20 precision Laser Range Finder as manufactured by Sierra Pacific Corp. of Las Vegas, Nev. and the LEICA RANGEMASTER 1200 Leica Laser Rangefinder (LLR) 1200 as manufactured by Leica in Koeln Germany. The distance to target 11 is then communicated to the processor 27. Once the distance information is received, then the processor 27 accesses the trajectory information storage and retrieval means 31 for the degree of prismatic shift required for the given distance and projectile. Moving the gun 9 to align the site 7 with the target 11 will cause the gun 9 to be positioned to correct for the trajectory characteristics of the projectile. the trajectory information storage and retrieval means 31 may in its simplest form be a chart used by the operator or, more preferably, may be any commercially available or proprietary database known to those skilled in the art, such as the Ballistic Explorer Version 5.5 available from Oehler Research, Inc. from Austin, Tex.<http://www.dexadine.com/bexw.html>, the Infinity version 5.0 Exterior Ballistic Software from Sierra Bullets of Sedalia, Mo., and the BALLISTIC BASICS 7.5 Pro-Elite Edition from BazoeSoft of Kill Devil Hills, NC <http://huntingcorner.com/bazoesoft/index.htm>. The shift information may be in the form of a look-up-table. Once the processor 27 receives the distance information from the range finder 29, it queries the storage and retrieval means 31 for the degree of prism shift required for the given distance. In a preferred embodiment, the storage and retrieval means 31 stores the trajectory characteristics, including windage and drop characteristics, for the projectile particular to the gun 9. In an alternate embodiment, the storage and retrieval means 31 stores prism shift information for several projectiles, including those that may be fired from the gun 9, thereby permitting the range compensator 5 to be mounted on the gun 9, removed and mounted on a second gun. In a further embodiment, the processor 27 also receives a measure of wind speed. The processor 27 then retrieves the prism shift information corresponding to the given projectile being fired from the determined distance in the measured wind conditions.

Once the required prism shift is determined, the processor 27 sends a signal to the controller 33 for the Risley prism pair 13, which is operably connected to the rotator 19 to effect rotational shift of the Risley prism pair 13 corresponding to the required amount of refraction. In doing so, the component prisms 21 and 23 are rotated between an unrefracted range finding position in which the “line of fire” 35 required to ensure the projectile strikes the target 11 is determined and a refracted firing position in which the “path of light” 17 extending between the site 7 and the target 11 is refractively deviated to maintain the target 11 centred with the site when the gun 9 is positioned along the required the “line of departure” 35.

In its simplest form, the “processor” may be the operator of the gun, the trajectory information may be looked up on a chart and the rotator manually operated. In this arrangement, indexing markings, such as degree markings, are desirable in order to correlate trajectory adjustment with prism position.

One Risley Prism Pair Refraction

Referring to FIG. 1, in the one Risley prism pair embodiment, the rotators 19 and 37 effect the rotational shift by a combination of counter-rotation and co-rotation ofthe prism components 21 and 23 and the Risley prism pair 13, respectively.

The rotator 19 includes a first motor that is rotationally coupled to both prisms 21 and 23 in the Risley prism pair 13 to cause equal but directionally opposite rotation of the prisms 21 and 23 about the axis 25 in response to activation of the first motor. The rotator 37 includes a second motor that is rotationally coupled to both the prisms 21 and 23 to cause simultaneous and equal co-rotation of the Risley prism pair 13 in response to activation of the second motor.

In an alternate embodiment of the invention, the rotator 19 includes first and second motors. In lieu of the second rotator 37. The first motor of rotator 19 is rotationally coupled to both prisms 21 and 23 in the Risley prism pair 13 to cause equal but directionally opposite rotation of the prisms 21 and 23 about the axis 25 in response to activation of the first motor; and, the second motor of rotator 19 is rotationally coupled to both the prisms 21 and 23 to cause simultaneous and equal co-rotation ofthe Risley prism pair 13 in response to activation of the second motor.

Two Risley Prism Pair Refraction

In a preferred embodiment, the compensator 59 consists oftwo fixed Risley prism pairs 13 and 67, each respectively effecting vertical and lateral refraction.

Referring to FIG. 2, the range compensator 59 includes a first Risley prism pair 13 for windage compensation and a second Risley prism pair 67 for drop compensation. Alternately, the Risley prism pair 13 may be used for drop compensation and the Risley prism pair 67 may be used for windage compensation. In each of the respective prism pairs 13 and 67, the first and second Risley prism pairs are counter-rotated by their respective rotators 19 and 61 in effecting the rotational shift. The respective rotators 19 and 61 are motors that are rotationally coupled to each prism in the respective Risley prism pairs 13 and 67 to cause equal but opposite rotation of the prisms about the axis 25 upon activation of the respective motors.

The Risley prism pair 13 with its prism pair components 21 and 23 being placed base-to- apex laterally will have a zero effect in an unrefracted position. Counter rotation of these prisms will introduce increasing amounts of prism power vertically. The resultant vertical prismatic effect is additive, while the resultant lateral prism effects are compensatory (component prism powers are equal and opposite to give zero lateral prismatic effect). The direction of the prismatic effect (base up or base down) will depend on the direction of counter rotation.

The Risley prism pair 67 with its prism pair components 63 and 65 being placed base-to-apex vertically will have a zero effect in an unrefracted position. Counter rotation of these prisms will introduce increasing amounts of prism power horizontally. The resultant lateral prismatic effect is additive, while the resultant vertical prism effects are compensatory (component prism powers are equal and opposite to give zero vertical prismatic effect). The direction of the prismatic effect (base right or base left) will depend on the direction of counter rotation.

The present invention is defined by the claims appended hereto, with the foregoing description being illustrative of the preferred embodiments of the invention. Those of ordinary skill may envisage certain additions, deletions and/or modifications to the described embodiments, which, although not explicitly suggested herein, do not depart from the scope of the invention, as defined by the appended claims.

List of Parts

-   -   5—Range Compensator     -   7—Gun Sight     -   9—Gun     -   11—Target     -   15—(RPP) Risley Prism Pair     -   15—Mounting Means     -   17—Path of Light     -   19—Rotator of 21, 23     -   21—Prism 1     -   23—Prism 2     -   25—Axis of Rotation     -   27—Processor     -   29—Range Finder     -   31—Trajectory Means     -   33—Controller for 13     -   34—Trajectory Path     -   35—Line of Departure     -   37—Second Rotator for RPP 13     -   39—Base of Prism 21     -   41—Apex of Prism 21     -   43—Base of Prism 23     -   45—Apex of Prism 23     -   47—Vertical Shift     -   49—Lateral Shift     -   51—Image Rotation Path     -   53—Degree of Rotation (Lateral)     -   55—Unadjusted Rotation Image     -   57—Adjusted Rotation Image     -   59—Range Compensator—Alternative Embodiment     -   61—Rotator for 61, 63     -   63—Prism 1     -   65—Prism 2     -   67—Second Risley Prism Pair     -   —Beam of Light     -   —Controller for 59     -   —Degree of Rotation (Vertical) 

1. A range compensator for a gun sight which enables said gun sight to appear “on target” when an associated gun is deviated from “line of sight” orientation with said target to allow for trajectory characteristics of a projectile to be launched from said gun, said compensator comprising: at least one Risley prism pair; mounting means for mounting said Risley prism pair to at least one of the gun and the sight between said sight and said target to allow refractive deviation of a path of light extending between said sight and said target; at least one respective rotator associated with each said Risley prism pair for rotating each prism in said Risley prism pair in at least opposite relative directions about an axis generally aligned with said path to cause said refractive deviation; a processor; a range finder communicating with said processor for determining the distance to said target of said gun and informing said processor of said distance; trajectory information retrieval and storage means communicating with said processor for providing information concerning said trajectory characteristics to said processor; said processor comparing said trajectory characteristics with said distance and determining a prism shift based thereon; said prism shift corresponding to an amount of refraction which will cause said sight to view a location relative to said target where said projectile would be expected to strike at said distance were said gun pointed directly at said target whereby moving said gun to align said sight with said target will cause said gun to be positioned to correct for said trajectory characteristics; said processor sending a signal to a respecting controller operably connected to each said rotator to effect rotational shift of said Risley prism pair corresponding to said amount of refraction.
 2. The range compensator of claim 1 wherein: said processor includes input means for wind speed; said trajectory characteristics include windage and drop characteristics; and said prism shift accommodates both windage and drop.
 3. The range compensator of claim 2 wherein: said at least one Risley prism pair includes a first Risley prism pair for windage compensation and a second Risley prism pair for drop compensation; each said prism in each said first and second Risley prism pairs are counter-rotated by said respective rotator in effecting said rotational shift.
 4. The range compensator of claim 3 wherein: each said respective rotator is a motor rotationally coupled to each said prism in said Risley prism pair to cause equal but opposite rotation of said prisms about said axis upon activation of said motor.
 5. The range compensator of claim 2 having one said Risley prism pair and wherein said rotator effects said rotational shift by a combination of co-rotation and counter-rotation of said Risley prism pair.
 6. The range compensator of claim 5 wherein: said rotator includes first and second motors, said first motor is rotationally coupled to both prisms in said Risley prism pair to cause equal but directionally opposite rotation of said prisms about said axis in response to actuation of said first motor; and, said second motor is rotationally coupled to both said prisms to cause simultaneous and equal co-rotation of said prisms in response to activation of said second motor.
 7. The range compensator of claims 1, 2, 3, 4, 5 or 6 wherein said gun sight is a laser sight and said at least one Risley prism pair refracts a laser beam emanating from said laser sight.
 8. The range compensation of claims 1, 2, 3, 4, 5 or 6 wherein said gun sight is a telescopic sight.
 9. A range compensator for a gun sight having an associated gun positionable for launching a projectile along a “line of departure” comprising: at least one Risley prism pair, the prisms being rotatable in at least opposite relative directions about a common axis; mounting means for mounting the Risley prism pair to at least one of the gun and the sight between the sight and a target at a distance for allowing refractive deviation of a path of light extending between the sight and the target; at least one respective rotator associated with each Risley prism pair for rotating each prism in the Risley prism pair about the axis, the axis being generally aligned with the path, the prisms being rotatable between an unrefracted range finding position in which the “line of departure” required to ensure the projectile strikes the target is determined and a refracted firing position in which the path of light extending between the sight and the target is refractively deviated to maintain the target centered with the sight when the gun is positioned along the required “line of departure”; and, indication means for determining the degree of refractive deviation.
 10. The range compensator of claim 9 further comprising: a range finder for determining the target distance; a prism rotation retrieval and storage means, the prism rotation retrieval and storage means for providing the degree of prism pair rotation required for rotating the prisms of the Risley prism pair to the refracted firing position and communicating the required degree of prism pair rotation to an operator; a respective controller operable by the operator and connected to each respective rotator to effect rotation of the Risley prism pair by the require degree of rotation. 